This invention relates in general to electrostatography and, in particular, to a process for fabricating electrostatographic imaging members.
In electrostatography, an electrophotographic imaging member is imaged by first uniformly electrostatically charging its surface. The photosensitive imaging member is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer, while leaving behind an electrostatic latent image in the non-illuminated areas. The electrostatic latent image is then developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image is transferred from the imaging member directly or indirectly to a support such as paper. This imaging process can be repeated many times with reusable imaging members.
The electrophotographic imaging member may be a plate, drum, belt or the like containing the photoconductive insulating layer on a conductive layer. This invention relates to a process for fabrication of substrates which are useful as photoreceptor belts for use in electrostatography.
Flexible organic photoreceptors in the form of belts are manufactured by coating a web and thereafter shearing the web into segments and forming the segments into belts by welding opposite ends. Since the resulting welded seam on the photoreceptor disrupts the continuity of the outer surface of the photoreceptor, the seam must be indexed so that it does not print out during imaging cycles. However, efficient stream feeding of paper and throughput are adversely affected because it is necessary to detect where the seam is located within the length of each sheet of paper. The mechanical and optical devices required for indexing add to the complexity and cost of equipment and reduce the available design flexibility. Welded belts are also less desirable for electrophotographic imaging systems because the seam forms a weak point in the belt and then collects toner debris during cleaning, particularly with wiper blade cleaning devices.
U.S. Pat. No. 4,711,833, to McAneney et al., Dec. 8, 1987, relates to a process for fabrication of a seamless belt. The process comprises providing a mandrel coated with a release coating, depositing a polymer by electrostatic spraying, melting the polymer and cooling the polymer. The resulting seamless belt is removed from the mandrel prior to or after application of a ground plane layer, photogenerating layer and charge generating layer. After formation of the coated or uncoated belt, air pressure is applied to the interior of the mandrel. The air passes through holes at one end of the mandrel to lift and break the adhesive bond between the inside surface of the seamless coated or uncoated belt and the surface. The air pressure is then released and the seamless coated or uncoated belt is slipped off the mandrel.
U.S. Pat. No. 4,747,992, to Sypula et al., May 31, 1988, relates to a process for forming a seamless belt comprising forming at least one thin uniform fluid coating of a film-forming polymer on a cylindrical mandrel having a larger mass, a lower thermal conductivity, or both a larger mass and a lower thermal conductivity than the film-forming polymer. The mandrel further has a critical surface tension greater than the surface tension of the fluid coating. The mandrel is coated and then both the mandrel and the coating are heated to a temperature above the apparent T.sub.g of the coating to expand the coating and mandrel. The coating is cooled below the apparent T.sub.g of the solid coating. The mandrel is then cooled whereby the mandrel contracts at a greater rate than the coating to effect separation between the mandrel and the coating. Fluid air or liquid may be introduced at one or both ends of the mandrel between the mandrel surface and the positive belt to reduce adhesion between the mandrel and the coating to facilitate removing the coating from the mandrel.
U.S. Pat. No. 5,100,628, to Griffiths et al., Mar. 21, 1992, teaches a method and apparatus for coating photoreceptors. Prior to coating, an elastically deformable material is placed around the external surface of an mandrel to accommodate a belt. The thickness of the mandrel is such that when the belt is placed, the deformable material is deformed and engages the interior surfaces of the belt facing the mandrel. As a result of heating and cooling during the coating process, the belt contracts and expands at a different rate than the mandrel. After coating, the coated belt is removed.
U.S. Pat. No. 5,167,987, to Yu, Dec. 1, 1992, relates to a process for fabricating an electrostatographic imaging member wherein a flexible substrate of a solid thermoplastic polymer is provided. An imaging layer coating including a film forming polymer is formed on the substrate. The coating and substrate are heated, then cooled. Sufficient predetermined biaxial tension is applied to the substrate while the energy layer coating and substrate are at a temperature greater than the glass transition temperature of the imaging layer coating. Application of the biaxial tension substantially compensates for all dimensional thermal contraction mismatches between the substrate and the imaging layer during cooling.
Japanese Laid-Open Patent Application No. 3-144458, Jun. 19, 1991, discloses a method of removing a coated membrane at the end of a drum wherein a laser beam is used to irradiate the membrane at a wavelength capable of burning and sublimating a coating formed on the outer circumferential surface of the drum. A suctioning device is disposed at the lower end of the drum to aid in removing the membrane from the drum surface.
Xerox Disclosure Journal, Vol. 17, No. 2, March/April, 1992, pages 95-96, discloses a continuous horizontal coating system for the manufacture of organic and alloy coated photoreceptors. The system includes various stations arranged in succession. The stations provide for operations such as material handling, vacuum and/or spray deposition, substrate drying and load/unload steps. The system provides for transporting a workpiece along a guide path via a linear motion system. The linear motion system may include an air film suspension/rotation/axial displacement system.
U.S. patent application Ser. No. 08/176,973, to Mastalski, now U.S. Pat. No. 5,413,810 filed on the same day as the present application, discloses a method of fabricating electrostatographic imaging members. An endless substrate is elastically stretched over a hollow cylindrical elongated support mandrel. The mandrel is formed of a porous material. Fluid is applied under pressure through the mandrel to form a layer of fluid between the outer surface of the mandrel and the inner surface of the substrate. The flow of fluid is manipulated to axially displace and to rotate the substrate on the outer surface of the mandrel. The flow of fluid is manipulated to orient a selected portion of the surface of the substrate to an angle to a direction of application of a coating. The temperature of fluid is manipulated to assist in substrate temperature control at steps of the coating and drying process.
The invention provides a method for processing a belt to produce a seamless belt with a uniform thermal history throughout. The invention also provides a method for obtaining photoconductive belt imaging members having uniform thermal history and uniform electrophotographic properties. The invention facilitates mounting and removal of the belt on a mandrel. The invention further provides a method for obtaining a photoconductive belt imaging member in which mounting of the belt on the carrier and removal therefrom is facilitated. The invention additionally provides a carrier for maintaining uniformly close thermal contact with the belt or photoconductive imaging member during its processing.